Graphic methods in heart disease / By John Hay ... ; with an introduction by James Mackenzie.

  • Hay, John
Date:
1909
Catalogue details

Licence: In copyright

Credit: Graphic methods in heart disease / By John Hay ... ; with an introduction by James Mackenzie. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    One must also remember that when the heart is excited by a stimulus sufficiently strong to initiate a contraction, it responds with the maximum contrac- tion possible at the time, irrespective of the intensity of the stimulus; its contraction is all or nothing. Again one must not forget that during, and for a short time after systole, the heart is in a refractory con- dition of varying duration in which no further con- traction can be obtained on stimulation. Immediately after systole all the functions of the myocardium, with the exception of tonicity, are in abeyance. The myocardium is then inexcitable, its conducting power is lost, its contractility has disap- peared, and the stimulus matter has been used up by the immediately preceding systole. With diastole all these functions begin to improve; generally the improvement is uniform, and by the time there is sufficient stimulus matter to excite the muscle to another contraction, the contractility and conduc- tivity are again normal. This period of rest after systole is necessary to enable each function to fully recover itself, and it is easy to understand that under abnormal conditions one or more functions may be depressed and require a longer period for their com- plete restoration. • Further, these functions of the cardiac muscle are not possessed in an equal degree by all the fibres lihroughout the heart, but in particular regions of
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